In recent years, development of applications that require delay time reduction (delay critical) has been considered. Examples of such applications that require delay time reduction include autonomous vehicle driving, augmented reality applications in smart glasses, or inter-machine communication.
In 3GPP, in order to develop these applications, latency reduction for reducing the packet data latency has been studied (see Non-Patent Literature 1). In latency reduction, shortening (reducing) the length of a transmission time interval (TTI) (TTI length), which is the time unit for transmission and reception of data, to be a time length between 0.5 msec and one orthogonal frequency division multiplexing (OFDM) symbol has been considered. Note that, the traditional TTI length is 1 msec, which is equal to the unit called “subframe.” One subframe is composed of two slots (one slot has a time length of 0.5 msec). One slot is composed of seven OFDM symbols for normal cyclic prefix (CP) and of six OFDM symbols for extended CP.
FIG. 1 illustrates an example of shortened TTIs for normal CP. When the TTI length is 0.5 msec (=1 slot), two TTIs are set per msec. When one slot is divided into a TTI composed of four OFDM symbols and a TTI composed of three OFDM symbols, four TTIs are set per msec. When the TTI length is one OFDM symbol, fourteen TTIs are set per msec.
Shortening the TTI length makes it possible to reduce latency for CQI reporting and thus to increase the frequency of CQI reporting, which is advantageous in that the difference between CQI reporting and actual channel quality is reduced.